Hello Poul_Puzzle,
We understand you're experiencing an issue with your Music app, and we'd like to get you pointed in the right direction for a resolution. Get started by reviewing the guidance below:
Log out, sleep, wake, restart, or shut down your Mac
If an app freezes or quits unexpectedly on Mac
These articles contain great steps for resolving issues with any app that is not working as expected. If the issue should persist, isolate further with safe mode as outlined here: How to use safe mode on your Mac
This article contains additional steps for if the issue does or does not persist.
Take care!